MORPHOLOGICAL EFFECTS OF CROWDING 329 



results as those in an open outdoor cage with lower humidity. The 

 same results were obtained in the hot midsummer as in the cooler 

 autumn. This eliminated to some degree the factors of season, il- 

 lumination, and temperature. Further, crowding experiments car- 

 ried on in darkness produced migratoid coloration just as did rearing 

 nymphs in open-air cages. Uvarov, in commenting on these experi- 

 ments, thinks that the results are due to influences, as yet unknown, 

 connected with the density of the larvae but not concerned with 

 the density of the eggs or of the adults. One wonders whether the 

 question of nematode infestation and its effects has been carefully 

 checked in this work. Plotnikov (1927; vide Uvarov, 1928) has 

 done work that confirms his earlier results that rearing under 

 crowded or isolated conditions causes the changes above recorded; 

 but he now regards these as aberrations, not as true transformations. 

 The intermediate forms found in nature he interprets as hybrids 

 between the two distinct races. These so-called "hybrids" do not 

 differ in appearance from intermediate forms produced by cultural 

 methods. In this connection we should record that Faure reports 

 having seen a small, solitary-phase male of L. pardalina copulating 

 with a large, swarm-phase female. 



Faure (1923), working on the South African locust Locustana 

 pardalina, observed transitions from the swarming phase to the 

 solitary phase. Eggs collected from a field, where they had "in all 

 probability" been deposited by a swarm, hatched out the usual 

 black of the swarming nymphs of the first instar. If a number of 

 these, some 60 or more, were kept together, swarm-phase colors 

 held during the succeeding instars. If small numbers, not more 

 than 10 or 12, were kept together in a cage, the color changed to 

 that common for the solitary-phase nymphs after the first molt, and 

 remained so during subsequent molts. The opposite change, from 

 solitary to swarm phase, came on more gradually with crowding. 

 Although without definite evidence, Faure believes, as a result of 

 field and laboratory observations, that about 300 in a group will 

 produce swarm-phase characteristics. Faure reconstructs the ap- 

 pearance of these two phases in nature as follows : After an epidemic 

 of swarm-phase locusts, great numbers are kiUed off by man or other 



